1. Field of the Invention
This invention relates to photographic film elements and more particularly to photographic elements coated on a support and having an opaque, protective backing layer coated thereon. Still more particularly, this invention relates to a photographic element containing an opaque, protective backing layer that can be removed in the fluids used during the processing step whereby the photographic element is fixed. Even more particularly, this invention relates to opaque, removable protective backing layers that can be conveniently used without altering the sensitometric characteristics of the photographic element coated on the opposite side of the support.
2. Description of the Prior Art
The addition of so-called "backing layers" to one side of a film support containing a photographic silver halide layer coated on the other side of the support, is well-known in the art. These layers are applied for various reasons. They are applied as anti-halation layers, anti-friction layers, anti-static layers and protective layers, for example. Carbon black is sometimes incorporated as an opacifying agent for anti-halation purposes, as described in U.S. Pat. No. 2,271,234, or for providing an opaque backing layer for diffusion transfer type photographic elements, whereby a reusable negative can be obtained, as explained in U.S. Pat. No. 3,677,790. U.S. Pat. No. 3,511,660 points out, however, that carbon black has a deleterious effect on the sensitometric properties of the photosensitive silver halide layer of photographic film. This is believed to be due to sulfur and trace metal impurities present in commercial carbon black which act as fogging agents for silver halides. The problem usually occurs when the photosensitive silver halide emulsion layer comes in contact with the backing layer when the element is rolled up, in the case of a photographic film.